I may be wrong, but there are two things I noticed. First you state thate you do not have a good fresh air supply. This is critical to plant growth, however because the onset was so quick I discount this as the real problem, but it does need to be addressed some time. What I am seeing ( without good pictures of the whole plant ) is a result of overwatering. Befor you water again, when the pots are fairly dry, gently remove the pot and check the roots. Are they a nice white or light tan in color? Or are they a dark brown or have blackish areas. If so theat would be an indication of root rot. This is a fungas that attacks the roots and is most often caused by overwatering. The cure is fairly simple. If you have access to a good hydro store then get a bottle of 28% hydrogen peroxide. Using 3 to 5 ml. of h2o2 to one gal of water flush the heck out of them. Make sure that the entire soil medium is saturated with the water/h202 solution. Then put them back in the flower room and do not water until the pot is noticably lighter in weight. Or until the plants are crying for water. At this point you should see a noticable difference in the progression of the problem. The damaged leaves will not recover, however the remainder of good leaves should show signs of returning health. You might add a bit of cal/mag to the water on first watering as well.

just my 2 cents worth.